(Not Applicable)
The present invention relates generally to oxygen delivery systems and more particularly to a closed loop system and method for automatically delivering fractionally inspired oxygen (FiO2).
Very low birth weight infants often present with episodes of hypoxemia. These episodes are detected by arterial oxygen saturation monitoring by pulse oximetry (SpO2) and are usually assisted with a transient increase in the fraction of inspired oxygen (FiO2).
Given the rapid onset and frequency at which most of these episodes of hypoxemia occur, maintaining SpO2 within a normal range by manual FiO2 adjustment during each episode is a difficult and time-consuming task. Nurses and respiratory therapists respond to high/low SpO2 alarms. Under routine clinical conditions, the response time is variable and the FiO2 adjustment is not well defined. This exposes the infants to periods of hypoxemia and hyperoxemia which may increase the risk of neonatal chronic lung disease and retinopathy of prematurity.
Thus, a need exists for a system that can automatically adjust FiO2. Prior art systems exist which automatically adjusts FiO2. Such systems have had positive results. However, existing systems fail to respond to rapid SpO2 changes and require manual intervention. Thus, a need exists for an automated system for adjusting FiO2 which will respond to rapid SpO2 changes. The system should not require manual intervention, but should allow for manual intervention, if desired. The system should also allow for gradually weaning the FiO2 as soon as an episode begins to resolve.
In accordance with the present invention, a system is provided for delivering fractionally inspired oxygen (FiO2) to a patient. The system includes a device, such as a pulse oximeter, for obtaining an arterial hemoglobin oxygen saturation signal (SpO2). An algorithm uses the SpO3 to determine the appropriate FiO2 to deliver to the patient. The algorithm adjusts the FiO2 level of an air-oxygen mixer of an oxygen delivery device, such as a mechanical ventilator.
In accordance with other aspects of the invention, SpO2 levels, including a target (normoxemia) range, are defined. SpO2 values above the normoxemia range are considered to be hyperoxemic and values below the normoxemia range are considered to be hypoxemic.
In accordance with further aspects of the invention, a determination is made as to whether the SpO2 signal is a valid signal. If the SpO2 signal is not a valid signal, the FiO2 to be delivered to the patient is determined based on a backup value. If the SpO2 signal is a valid signal and closed loop mode is not enabled, the FiO2 to be delivered to the patient is determined based on a backup value. If the signal is valid and closed loop mode is enabled, the FiO2 to be delivered to the patient is determined based on the current SpO2 and the trend. The trend is determined by calculating a slope using previous SpO2 values. The determined FiO2 is then delivered to the patient, for example, using a ventilator or an air-oxygen gas mixer.
In accordance with still further aspects of the invention, a user interface is provided. The user interface displays status information. The user interface also displays alerts. The user interface can also be used to view and modify user settings/parameters.